Im making a Belgian Crand Cru Reserve, with an OG=1.107 and a target FG=1.023. Yeast was pitched on sat 7/26 at 530pm EST. Primary was roiling aggressively until 9 PM 7/27. By 730 AM 7/28, primary has stopped.

Gravity check reveals 1.043-1.045. Pitch rate was 15 Mil Cells/ml. I suspect ran out of O2 for a beer this big. Should I aerate to introce a little more oxygen?

I don't mean to insult your intelligence or your brewing knowledge, but are you _SURE_ it has stopped fermenting. It's not unusual to get a very vigorous fermentation during the first 24 hours or so, and then have it slow down dramatically. Are you using an air lock? Sometimes they will bubble only once every minute or two, but the fermentation is still active. Also, you don't mention how many gravity readings you took and over what interval. At the very least, I'd take a gravity reading and then another one maybe 12 hours later to see if there is any change, and then another again in 12 more hours just to be sure. While you did under-pitch your yeast slighty (Mr. Malty's Pitching Rate Calculator indicates 19 mil/ml for that O.G.), it is not all that different from the 15 mil/ml that you pitched, so I'd be surprised if the yeast were overwhelmed, expecially if you employed any aeration of your wort before pitching your yeast (I had actually completely stopped aerating my wort when pitching a sufficient yeast count, and never had any stuck fermentations, but was later advised that my beer would still be better if aerated first). By the way, here is a link to Mr. Malty's Calculator, for any who don't have it: http://www.mrmalty.com/calc/calc.html

Now, if the fermentation has stopped, it is because your yeast is tired or can't handle the alcohol level, and not because there is not more oxygen in your wort at this point (there really shouldn't be anyway at this point), so aerating your wort is not going to change the condition of your yeast and is likely to cause oxidation problems with your brew, so I definitely would not recommend doing that. Note that some brewers recommend re-aeration in the fermenter, but I believe that this is intended to happen something like 12 hours after yeast is pitched and certainly not more than 48 hours later. I think the only solution to your problem is to pitch some additional yeast without aerating. You could even do that immediately, since it shouldn't hurt your beer even if you are mistaken about the stuck fermentation. I think some folks will sometimes stir the beer slightly to try to rouse flocculated yeast, but personally I can't see how that will do a whole lot of good because it doesn't address the reason the yeast flocculated in the first place; but I've never tried that so I can't say for certain.

EDIT: Just thought of something else I'd add; you didn't specify whether you used extract or grains, and if the later, what you grain bill was and mash schedule. Your current attenuation is only 59%, which is VERY low, but I have heard of some brewers getting attenuation that low with some extracts. Also, you now have an alcohol content of 8.4%, so if you practiced good sanitation, you should be safe in letting your beer sit for a couple of days and then checking the gravity again.

Just my two cents. Good luck. Let us know how it turns out.

Bill Velek

Last edited by billvelek on Mon Jul 28, 2008 10:47 pm, edited 1 time in total.

Robust fermentation resumed 3-4 hrs after aeration. The fermentation was near zero. No bubbles produced in several minutes.

I acutally called Wyeast and their Micro Bio recommended further agiatation. If that failed, then add yeast.

I failed to note that im crossing two strains on this one. One a fast starter, and the other is not. Its likely that the fast starter consumed a good chunk of the O2 and became exhausted. After aeration, the other yeast picked up.

manplant wrote:Robust fermentation resumed 3-4 hrs after aeration. The fermentation was near zero. No bubbles produced in several minutes.

I acutally called Wyeast and their Micro Bio recommended further agiatation. If that failed, then add yeast.

I failed to note that im crossing two strains on this one. One a fast starter, and the other is not. Its likely that the fast starter consumed a good chunk of the O2 and became exhausted. After aeration, the other yeast picked up.

I appreciate your help.

I'm glad it seems to be working out for you. If Wyeast recommends agitation to rouse the yeast, then I guess there must be some merit in doing so despite my skeptical remark; flocculation is not merely that yeast settle to the bottom, but they actually group and cling together, so I was skeptical because ... 1.) I believed stirring probably doesn't really break them apart, and ... 2.) other than releasing some of the concentration of CO2 (assuming aeration doesn't occur, too), I fail to see what has changed in the wort to prevent the yeast from re-flocculating.

Now, you said that you aerated and it fixed the problem; first, I'm not sure what aeration does for 'tired' yeast, although it will cause some reproduction assuming the yeast are healthy enough to reproduce; second, you did not say that Wyeast recommended aeration. Not to quibble, but if Wyeast said "agitation", that is not the same as aeration. And even if Wyeast _HAD_ said aeration, ... well ... they know a lot about yeast but do they know much about brewing beer? When you tell me later that the beer turned out okay without any signs of oxidation, then I'll feel better about aerating after 48+ hours, but meanwhile I would not recommend to anyone that they ever aerate beer that has already fermented for that long. I hope your beer turns out great ... and it very well could ... but aeration at this late stage flies directly in the face of everything that I've ever read about brewing.

Bill,
I appreciate your follow up. They used the term agitation, with the purpose of adding more o2. I tend to believe that 1388 (2 packs) started fast as it should, then got exhausted. I wisked in more air, but by that time the 3787 Trappist was beginning. So the verdict was out on if I really needed O2 or not. However, the fermentation is still going strong. The air introduced by the wisking likely will be entirely consumed by the added fermentation.

Timing of these two yeasts makes this a tough one. The last batch I made had a 50/50, so it was easy. This one was 66/33. I can smell the 3787 offgassing currently.

Be sure to let us all know how this batch turns out. I'm curious whether having two different yeasts in the fermentation together results in anything different than two separate single-yeast fermentations which are then blended in exact proportions at bottling time. That would eliminate your difficulty with timing.

I'm still not convinced that aeration after over 48 hours into the fermentation is a wise or advisable thing to do. Please let us know if there are any signs at all of oxidation in your beer. You sound like an experienced brewer who will be able to tell, so if you can't detect it then I'll be convinced.

Ill keep you posted. The imbalance on this one was possibly a bad idea.

I have tripel in the sec that was 50/50 1388 and 3787. Ive never had a belgian turn out that good out of the primary, so we will see.

I have a Wit in the keg that is almost gone that had a slight metallic taste to it the day or two after kegging. The local brewer says that could be some oxidation, but beyond that, Ive never had an issue.

Ive heard ascorbic acid added to the racking process to seconday or keg can absorb oxygen. What are your thoughts on this?

Ive only been brewing for a year, but I have an engineering degree and 15 years of expert level manufacturing process engineering experience. Brewing is a process. I went from a True Brew box to custom all grain recipes in 90 days. Im not an expert though, otherwise I wouldnt be asking some of the dumb q's I do.

you should check the seal on your fermenter...I had the same problem and found that the seal was not working...after I fixed the problem everything was fine...I had made 3 or 4 brews that quit working early but I always let it go a few more days, then went to secondary a little too early. now I have an understanding and don't have the same issues.
I am pretty sure you have the same problem...yeast don't just quit...

manplant, i know your post its a few years old, but i am having the same problem with a similar beer and did the same thing. The fermentation started back up nicely.
i was just curious how yours eventually turned out ?